pvmfw: instance: Store UUID in little endian

As instance.img seems to store UUIDs in little endian (even though the
most common UUID endianness seems to be BE), store the EntryHeader::uuid
with the same endianness so that it can be memcpy()-ed to the block
device as-is, allowing instance.img consumers to properly parse the
pvmfw UUID.

Bug: 249723852
Test: atest MicrodroidTests
Change-Id: I7c9c6ec2389c8473a6fa685e4b595629695b43e5
diff --git a/pvmfw/src/instance.rs b/pvmfw/src/instance.rs
index fbf2040..a974543 100644
--- a/pvmfw/src/instance.rs
+++ b/pvmfw/src/instance.rs
@@ -258,11 +258,11 @@
 
 impl EntryHeader {
     fn new(uuid: Uuid, payload_size: usize) -> Self {
-        Self { uuid: uuid.as_u128(), payload_size: u64::try_from(payload_size).unwrap().to_le() }
+        Self { uuid: uuid.to_u128_le(), payload_size: u64::try_from(payload_size).unwrap().to_le() }
     }
 
     fn uuid(&self) -> Uuid {
-        Uuid::from_u128(self.uuid)
+        Uuid::from_u128_le(self.uuid)
     }
 
     fn payload_size(&self) -> usize {